Presentation Transcript

Electromagnetic Waves :

Electromagnetic Waves

About Electromagnetic Waves :

About Electromagnetic Waves When you listen to the radio, watch TV, or cook dinner in a microwave oven, you are using electromagnetic waves.
Radio waves, television waves, and microwaves are all types of electromagnetic waves. They differ from each other in wavelength. Wavelength is the distance between one wave crest to the next.

Properties of Electromagnetic Waves :

Properties of Electromagnetic Waves Electromagnetic Wave- A transverse wave consisting of oscillating electric and magnetic fields at right angles to each other
The spectrum includes more than visible light- not all light is visible to the human eye
Light is a wave and also a particle

The Electromagnetic Spectrum :

Properties of the Electromagnetic Spectrum :

Properties of the Electromagnetic Spectrum Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom.
Did you know that electromagnetic waves can not only be described by their wavelength, but also by their energy and frequency? All three of these things are related to each other mathematically. This means that it is correct to talk about the energy of an X-ray or the wavelength of a microwave or the frequency of a radio wave. The electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, X-rays, and gamma-rays.

Different Frequencies and Wavelength :

Different Frequencies and Wavelength In visible light, the differences in frequency and wavelength account for the different colors. Just as red light has its own distinct frequency and wavelength, so do all the other colors. Orange, yellow, green, and blue each exhibit unique frequencies and consequently wavelengths. While we can perceive these electromagnetic waves in their corresponding colors, we cannot see the rest of the electromagnetic spectrum.
The differences in wavelength and frequency also distinguishes visible light from invisible electromagnetic radiation, such as X Rays.

Frequencies for different colors :

Frequencies for different colors Every electromagnetic wave exhibits a unique frequency, and wavelength associated with that frequency. For instance, this picture represents an electromagnetic wave corresponding to the color red.
Its frequency is 428 570 GHz (pronounced gigahertz), which can also be stated as 428,570 billion cycles per second. So when you look at red light, your eye receives over four hundred trillion waves every second!

Radio Waves :

Radio Waves Radio waves have the longest wavelengths in the electromagnetic spectrum. These waves can be longer than a football field or as short as a football. Radio waves do more than just bring music to your radio. They also carry signals for your television and cellular phones.
Objects in space, such as planets and comets, giant clouds of gas and dust, and stars and galaxies, emit light at many different wavelengths. Some of the light they emit has very large wavelengths - sometimes as long as a mile! These long waves are in the radio region of the electromagnetic spectrum.

Microwaves :

Microwaves Microwaves have wavelengths that can be measured in centimeters! The longer microwaves, those closer to a foot in length, are the waves which heat our food in a microwave oven.
Microwaves are good for transmitting information from one place to another because microwave energy can penetrate haze, light rain and snow, clouds, and smoke.
Because microwaves can penetrate haze, light rain and snow, clouds and smoke, these waves are good for viewing the Earth from space.

Infrared Light :

Infrared Light Infrared light lies between the visible and microwave portions of the electromagnetic spectrum.
Far infrared waves are thermal. In other words, we experience this type of infrared radiation every day in the form of heat! The heat that we feel from sunlight, a fire, a radiator or a warm sidewalk is infrared.
Shorter, near infrared waves are not hot at all - in fact you cannot even feel them. These shorter wavelengths are the ones used by your TV's remote control.
To make infrared pictures like the one below, we can use special cameras and film that detect differences in temperature, and then assign different brightnesses or false colors to them. This provides a picture that our eyes can interpret.

Visible Light Waves :

Visible Light Waves Visible light waves are the only electromagnetic waves we can see. We see these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light.
When white light shines through a prism, the white light is broken apart into the colors of the visible light spectrum. Water vapor in the atmosphere can also break apart wavelengths creating a rainbow.
Cones in our eyes are receivers for these tiny visible light waves. The Sun is a natural source for visible light waves and our eyes see the reflection of this sunlight off the objects around us. The color of an object that we see is the color of light reflected. All other colors are absorbed.

Ultraviolet Waves :

Ultraviolet Waves Ultraviolet (UV) light has shorter wavelengths than visible light. Though these waves are invisible to the human eye, some insects, like bumblebees, can see them!
Scientists have divided the ultraviolet part of the spectrum into three regions: the near ultraviolet, the far ultraviolet, and the extreme ultraviolet. The three regions are distinguished by how energetic the ultraviolet radiation is, and by the "wavelength" of the ultraviolet light, which is related to energy.
Our Sun emits light at all the different wavelengths in electromagnetic spectrum, but it is ultraviolet waves that are responsible for causing our sunburns.
Though some ultraviolet waves from the Sun penetrate Earth's atmosphere, most of them are blocked from entering by various gases like Ozone. Some days, more ultraviolet waves get through our atmosphere. Scientists have developed a UV index to help people protect themselves from these harmful ultraviolet waves.

X-Rays :

X-Rays When you get an X-ray taken at a hospital, X-ray sensitive film is put on one side of your body, and X-rays are shot through you.
Because your bones and teeth are dense and absorb more X-rays then your skin does, silhouettes of your bones or teeth are left on the X-ray film while your skin appears transparent.
Many things in space emit X-rays, among them are black holes, neutron stars, binary star systems, supernova remnants, stars, the Sun, and even some comets!

Gamma Rays :

Gamma Rays Gamma-rays have the smallest wavelengths and the most energy of any other wave in the electromagnetic spectrum. These waves are generated by radioactive atoms and in nuclear explosions. Gamma-rays can kill living cells, a fact which medicine uses to its advantage, using gamma-rays to kill cancerous cells.
Gamma-rays are the most energetic form of light and are produced by the hottest regions of the universe. They are also produced by such violent events as supernova explosions or the destruction of atoms, and by less dramatic events, such as the decay of radioactive material in space. Things like supernova explosions (the way massive stars die), neutron stars and pulsars, and black holes are all sources of celestial gamma-rays.

Speed of Electromagnetic Waves :

Speed of Electromagnetic Waves All electromagnetic waves move at the speed of light
Remember…
Speed= wavelength x frequency
Only the wavelength and frequency change
This change decides which type of electromagnetic wave it is (radio, gamma, etc.)

Speed of Light :

Speed of Light The speed of light in a vacuum= 2.99792458 x 108 m/s
The speed of light in air= 2.99709 x 108 m/s
We use 3 x 108 m/s which equates to 300 million meters per second!

Astronomy and the Spectrum :

Astronomy and the Spectrum By studying the electromagnetic emissions of objects such as stars, galaxies, and black holes, astronomers hope to come to a better understanding of the universe. Although many astronomical puzzles can only be solved by comparing images of different wavelengths, telescopes are only designed to detect a particular portion of the electromagnetic spectrum. Astronomers therefore often use images from several different telescopes to study celestial phenomena. Shown on the next slide is the Milky Way Galaxy as seen by radio, infrared, optical, X-ray and gamma-ray telescopes.

Milky Way Galaxy as seen by different rayed telescopes :

Milky Way Galaxy as seen by different rayed telescopes From top to bottom: Radio, Infrared, Visual, X Ray, and Gamma Rays